A variety of industrial robots have recently come into wide use in various fields. FIG. 3 is a side view illustrating one example of a horizontal articulated industrial robot installed on a floor and provided with a swiveling post.
In FIG. 3, numeral 1 denotes the post supported on a base 2 and capable of being swiveled within a predetermined rotational range (.theta.). Provided within the base 2 is a swiveling mechanism 21 for swiveling the post 1. Numeral 3 denotes a first arm (working arm) supported at the upper portion of the post 1 by a support shaft 4. A second arm 5 capable of being swiveled in the horizontal direction is attached to the distal end of the first arm 3, and the distal end of the second arm 5 is provided with a wrist 51.
Provided in the post 1 is a drive mechanism 6 for moving the support shaft 4 up and down within a predetermined range (Z) to control the height of the first arm 3.
FIG. 4 is a longitudinal sectional view of the post 1, in which numeral 7 denotes a drive motor having a motor pulley 71 for rotating a screw rod 61 of the drive mechanism 6 via the motor pulley 71, a belt 72 and a drive pulley 63, whereby a nut 62 threadedly engaged with the screw rod 61 is moved up and down to raise and lower the support shaft 4 and, hence, position the working plane of the arm. A movable brake element 81 is fixedly secured to the lower end of the screw rod 61. Attached to the bottom 11 of the post 1 is a fixed brake element 82 for braking rotation of the screw rod 61 by attracting the movable brake element 81 through the use of electromagnetism.
In order to prevent the support shaft 4 from being moved out of position by an external force or the like when the drive motor 7 has been stopped to hold the support shaft 4 at a prescribed height, the braking mechanism in the drive mechanism of the aforementioned kind is so adapted that the fixed brake element 82 attracts the movable brake element 81 to brake the rotation of the screw rod 61, thereby positioning the arms 3, 5 in a prescribed working plane.
In the above-described industrial robot, exchanging the belt 72 between the motor pulley 71 of drive motor 7 and the drive pulley 63 involves a difficult operation in terms of mounting the new belt since the movable brake element 81 is fixedly secured to the lower end of the screw rod 61. Inspecting the contact surfaces of the movable brake element 81 and fixed brake element 82 is a troublesome operation since the movable brake element 81 is fixedly secured to the screw rod 61 and the clearance between the two contact surfaces is small.